This invention relates to an in-situ cap for an integrated circuit device such as a micromachined device and to a method of making such an in-situ cap.
Conventional caps for integrated circuit devices such as micromachined devices are often used to protect and isolate. Typically the caps are made independently of the device itself and then attached after the device fabrication is completed. Often the cap is fabricated from silicon and fastened to the devices with an organic adhesive or with an inorganic glass or metal. While this approach can be satisfactory, it does require separate processes to make the caps and then to join them to the integrated circuit devices. One set of joining processes applies caps to integrated circuit devices before the wafers are singulated. This requires expensive wafer scale processes and equipment. Cap stress effects can cause yield loss if the process is not tightly controlled. However, a tightly controlled wafer level process protects the delicate micromachined devices early in the manufacturing process. Another set of processes applies the caps after singulation. This can be simpler to implement but it requires special precautions to avoid contamination during wafer singulation and other process steps. Still another approach eliminates the requirement for directly attaching caps to the integrated circuit devices by mounting and wire bonding the devices inside cavity packages. In essence, the next level package becomes the cap. This method often utilizes expensive hermetically sealed ceramic or metal packages. It also requires that the manufacturing facility maintain unusual cleanliness standards in order to avoid contamination during assembly of the delicate micromachined devices.
It is therefore an object of this invention to provide an improved in-situ cap for integrated circuit devices including micromachined devices and a method of making it.
It is a further object of this invention to provide such a cap and method which utilize the basic integrated circuit fabrication process to make the cap as well.
It is a further object of this invention to provide such a cap and method which provides the cap as an integrated in-situ part of the device itself.
It is a further object of this invention to provide such a cap and method which require no special or independent effort to make or install the cap.
It is a further object of this invention to provide such a cap and method in which the cap can be used to preserve a suitable environment within the cap such as a gas or liquid fill or a vacuum.
It is a further object of this invention to provide such a cap and method which protects the capped device immediately upon completion of the processing before any further handling including die separation, testing and handling.
It is a further object of this invention to provide such a cap and method which has much lower manufacturing cost.
It is a further object of this invention to provide such a cap and method in which post-processing is made easier because the devices are less vulnerable since they are capped at the end of wafer processing before die cutting.
It is a further object of this invention to provide such a cap and method which requires the same low temperature processing as the rest of the integrated circuit.
The invention results from the realization that a truly improved, more robust, simpler and less expensive in-situ cap for an integrated circuit device and method of making such a cap can be achieved by fabricating a cap in-situ on an integrated circuit device as a part of the integrated circuit fabrication process by forming a support layer on the integrated circuit device and then forming the cap structure in the support layer covering the integrated circuit element.
This invention features a method of fabricating an in-situ cap for a micromachined device including fabricating a micromachined element on a substrate with a sacrificial support layer intact and fabricating a cap sacrificial support layer over the micromachined element. The cap structure is formed in the sacrificial layers covering the micromachined element and the sacrificial layers are removed within the cap structure to release the micromachined element leaving an in-situ cap integral with the device.
In a preferred embodiment forming the cap structure may include forming a cap hole around the element. Forming the cap structure may also include filling the cap hole to form a cap wall and covering the sacrificial layers to form a top connected with the cap wall. The cap may be formed with at least one hole and removing the sacrificial layers may include introducing a release agent through the hole in the cap. The substrate may be formed with at least one hole and removing the sacrificial layers may include introducing release agent through the hole in the substrate. The cap hole may be closed to seal the cap. A fluid filler may be introduced through the cap hole into the cap surrounding the micromachined element. The cap hole may be closed to seal in the fluid. The cap hole may be small and the surface tension of the fluid may prevent its escape. Fabricating a cap may include forming a contact on the cap. The micromachined element may include a switch and the contact may be a terminal of the switch. Fabricating a cap may also include forming a gate electrode on the cap for operating the switch. The fluid may be a crosslinkable material; the volume in the cap may be a vacuum; the fluid may modify a surface inside the cap.
This invention also features a method of fabricating an in-situ cap for an integrated circuit device including fabricating an integrated circuit element on a substrate, forming a support layer over the integrated circuit element and forming a cap structure in the support layer covering the integrated circuit element.
In a preferred embodiment the method may further include removing the support layer within the cap structure.
This invention also features a micromachined device with an in-situ cap including a substrate, a micromachined element on the substrate and an in-situ cap integral with the substrate and covering the element. There is at least one conductor extending from the element under the cap through the substrate to an external terminal.
In a preferred embodiment, the cap may be filled with liquid; the liquid may be a dielectric. The micromachined element may include a switch; the cap may include a hole; the micromachined element may include an optical device; and the hole may be an optical port. The cap may include a contact; the micromachined element may include a switch; and the contact may be a terminal of the switch. The cap may include a gate electrode for operating the switch.
This invention also features a micromachined device with an in-situ cap including a substrate, a micromachined element on the substrate, and an in-situ cap integral with the substrate covering the element. The micromachined element may be an optical device and there may be an optical port for accessing the optical device. In a preferred embodiment, the port may be in the cap.
This invention also features a micromachined device with an in-situ cap including a substrate, a micromachined element on the substrate, and an in-situ cap integral with substrate and covering the element. There may be a liquid disposed in the cap.
In a preferred embodiment the liquid may be a dielectric.
This invention also features an integrated circuit device with an in-situ cap including a substrate, an integrated circuit element on the substrate, and an in-situ cap integral with the substrate and covering the element. At least one conductor may extend from the element under the cap through the substrate to an external terminal.
This invention also features an integrated circuit device with an in-situ cap including a substrate, an integrated circuit element on the substrate, and an in-situ cap integral with the substrate and covering the element. The integrated circuit element may be an optical device and there may be an optical port for accessing the optical device.
This invention also features an integrated circuit device with an in-situ cap including a substrate, an integrated circuit element on the substrate, and an in-situ cap integral with the substrate and covering the element. A liquid may be disposed in the cap.